Photomask reticle having multiple versions of the same mask pattern with different biases

ABSTRACT

A reticle includes at least two duplicate mask patterns each having a different bias. A reticle according to at least one embodiment of the invention includes a first mask pattern, a second mask pattern and a third mask pattern, each of the first mask pattern, second mask pattern and third mask pattern being duplicates of one another and having a different bias.

FIELD OF THE INVENTION

The present invention relates to photomasks used in semiconductor waferfabrication and methods of manufacturing the same. In particular, thepresent invention relates to photomasks with multiple versions of thesame mask pattern having different biases to compensate for processerrors that occur during exposure to form a semiconductor wafer.

BACKGROUND OF THE INVENTION

There are a wide variety of photomasks known in the art, as well asdiverse uses to which they can put, as described in, e.g., U.S. Pat.Nos. 6,472,107 and 6,567,588. Among the many types of photomasks used inthe semiconductor industry, binary and phaseshift photomasks are quitecommon. A typical binary photomask is comprised of a substantiallytransparent substrate 2 and opaque layer 4, in which a pattern isformed, as shown in a cross sectional illustration of an unprocessedbinary photomask in FIG. 1A. Further, the opaque layer 4 may also havean anti reflective (“AR”) coating 6. The pattern of the opaque materialin the opaque layer 4 and AR material in the AR coating 6 on thesubstantially transparent substrate 2 may be a scaled negative of theimage desired to be formed on the semiconductor wafer. For a typicalchrome on glass (“CoG”) or binary photomask, the substantiallytransparent substrate 2 is comprised of quartz. The opaque material 4 iscomprised of chromium (“Cr”) and the AR material is comprised ofchromium oxide (“CrO”).

A binary photomask used in the production of semiconductor devices isformed from a “blank” photomask. As shown in FIG. 1A, a prior art blankphotomask 1 is commonly comprised of at least four layers. The firstlayer 2 is a substantially transparent substrate, such as quartz,commonly referred to as the substrate. The next layer above thesubstantially transparent layer 2 is an opaque layer 4, which iscomprised of Cr in the case of a typical CoG photomasks. Thereafter,although not always necessary, there may be an AR layer 6 integral tothe opaque layer, which in the case of CoG photomasks is comprised ofCrO. A layer of photosensitive resist material 8 resides as the toplayer. In the case of CoG photomasks, the photosensitive resist material8 is typically a hydrocarbon polymer, the various compositions andthicknesses of which are well known in the art. Other layers may also bepresent for alternative reasons, as is described, for example, in U.S.Pat. No. 6,472,107. Similarly, other materials may be used as is wellknown in the art.

The desired pattern of opaque material to be created on the photomaskmay be defined by an electronic data file loaded into an exposure systemwhich typically scans an electron beam (E beam) or laser beam in araster fashion across the blank photomask. One such example of a rasterscan exposure system is described in U.S. Pat. No. 3,900,737. Otherimaging systems can be used that do not use raster scanning, such asshaped vector tools. As the E beam or laser beam is scanned across theblank photomask, the exposure system directs the E beam or laser beam ataddressable locations on the photomask as defined by the electronic datafile. In the case of a positive photoresist, the areas that are exposedto the E beam or laser beam become soluble, while the unexposed portionsremain insoluble. In the case of a negative photoresist, the unexposedareas become soluble, while the exposed portions remain insoluble. Asshown in FIG. 1B, after the exposure system has scanned the desiredimage onto the photosensitive resist material, the solublephotosensitive resist is removed by means well known in the art, and theinsoluble photosensitive resist material 8 a remains adhered to the nextlayer (e.g., the AR layer 6).

After undergoing the foregoing photolithographic process, as illustratedin FIG. 1C, the exposed layer of AR material 6 and the underlying layerof opaque material 4 are no longer covered by the photosensitive resistmaterial 8 a and are removed by a well known etch process. Only theportions of the layer of AR material 6 a and the layer of opaquematerial 4 a residing beneath the remaining photosensitive resistmaterial 8 a remain affixed to the substantially transparent substrate2. This initial or base etching may be accomplished by either a wetetching or dry etch process, both of which are well known in the art.

Another type of photomask used for transferring images to asemiconductor wafer is commonly referred to as a phaseshift photomask.Phaseshift photomasks are generally preferred over binary photomaskswhen the design to be transferred to the semiconductor wafer includessmaller, tightly packed feature sizes which are below the resolutioncapabilities of optical equipment being used. Phaseshift photomasks areengineered to be 180 degrees out of phase with light transmitted throughetched areas on the photomask so that the light transmitted through theopenings in the photomask is equal in amplitude.

One type of phaseshift photomask is commonly referred to as an embeddedattenuated phaseshift mask (EAPSM). Other types of phaseshift masks arealso known, and the teachings of the present invention may be equallyapplied thereto. As shown in FIG. 2A, a typical blank EAPSM 31 may becomprised of four layers. The first layer is a typically a substantiallytransparent material 33 (such as quartz, for example) and is commonlyreferred to as a substrate. The next layer is typically an embeddedphaseshifting material (“PSM layer”) 35, such as molybdenum silicide(MoSi), tantalum silicon nitride (TaSiN), titanium silicon nitride(TiSiN), zirconium silicon oxide (ZrSiO), or other known phasematerials. The next layer is typically an opaque material 37, such aschromium, which may optionally include an anti reflective coating suchas chromium oxynitride (CrON). The top layer is a photosensitive resistmaterial 39, as is well known in the art.

The method for processing a conventional EAPSM is now described. As withbinary photomasks, the desired pattern of the opaque material to becreated on the EAPSM is typically scanned by an electron beam (E beam)or laser beam in a raster or vector fashion across a blank EAPSM 31. Asthe E beam or laser beam is scanned across the blank EAPSM 31, theexposure system directs the E beam or laser beam at addressablelocations on the EAPSM. In the case of a positive photoresist material,the areas that are exposed to the E beam or laser beam become soluble,while the unexposed portions remain insoluble. In the case of a negativephotoresist, the unexposed areas become soluble, while the exposedportions remain insoluble.

As is done with binary photomasks and as shown in FIG. 2B, after theexposure system has scanned the desired image onto the photosensitiveresist material 39, the soluble photosensitive resist material isremoved by means well known in the art, and the insoluble photosensitiveresist material 39 a remains adhered to the opaque material 37. Thus,the pattern to be formed on the EAPSM is formed by the remainingphotosensitive resist material 39 a.

The pattern is then transferred from the remaining photosensitive resistmaterial 39 a to the opaque layer 37 and PSM layer 35 via well knownetching techniques, such as plasma assisted etch described above, byetching away the portions of the opaque layer and PSM layer not coveredby the remaining photoresist. After etching is completed, the remainingphotoresist material is stripped or removed as shown in FIG. 2C. Otherprocessing steps, such as partial or complete etching of the opaquelayer 37 a, may be further performed to complete the fabrication of thephaseshift photomask.

Photomasks are used in the semiconductor industry to transfer microscale images defining a semiconductor circuit onto a silicon or galliumarsenide substrate or wafer and the like. To create an image on asemiconductor wafer, the photomask is interposed between thesemiconductor wafer, which includes a layer of photosensitive material,and a stepper, which houses an energy source, such as a lamp or a laser.The energy generated by the stepper passes through the transparentportions of the substantially transparent substrate not covered by theopaque material (and, if utilized, the anti reflective and/or phaseshiftmaterial) and causes a reaction in the photosensitive material on thesemiconductor wafer. Energy from the stepper is prevented from passingthrough the opaque portions of the photomask. As with the manufacture ofphotomasks, when the photosensitive material is exposed to light it willreact. Thereafter, the soluble photosensitive material is removed usingprocesses well known in the prior art. The semiconductor wafer is thenetched in a manner similar to that described above. After furtherprocessing, a semiconductor product is formed.

As semiconductor chip features become exponentially smaller and thenumber of transistors per device become exponentially larger, largeburdens have been placed on lithography processes. Resolution ofanything smaller than a wavelength of exposure radiation is generallyquite difficult, and pattern fidelity can deteriorate dramatically insub-wavelength lithography. The resulting semiconductor features maydeviate significantly in size and shape from the ideal pattern drawnfrom the circuit designer. This will decrease process yield and increasecost of the overall photomask manufacturing process.

The semiconductor industry is driven by a desire to lessen processingtime and increasing process yield while maintaining or even reducingcurrent costs. In particular, regarding lithograpy techniques usingphotomasks, the semiconductor industry has attempted to reduce processerrors to increase yield by compensating for these process errors in thephotomasks themselves. For example, when an image is transferred to awafer by a 4× stepper tool using a photomask with a critical dimension(CD) of 100 nm, the resulting device layer on the wafer may have a linewidth of 28 nm. Accordingly, the semiconductor manufacturer will oftenrequest that the CD of the photomask be adjusted (or “biased”) so that,when the photomask pattern is developed on the semiconductor wafer, theresulting product will have the desired line width of 25 nm instead of28 nm.

As a further example, U.S. Patent Application Publication No.2003/0134205 (“the '205 application”) discloses a process formanufacturing a photomask in which, for each pitch within asemiconductor design, a bias needed at the pitch that maximizes a commonprocess window for all the pitches is calculated based on the givencritical dimension (CD) of the mask design. The '205 applicationcombines this biasing with optical proximity correction to appropriatelymodify the original layout of the photomask. However, techniques such asthat disclosed in the '205 application are costly and increaseturn-around time due to the required inspection steps and correctionanalysis.

Other techniques have been adopted to decrease cost of the photomaskmanufacturing process, which do not relate directly to reducing processerrors or increasing yield. Such techniques often involve using multiplemask patterns on a common reticle or plate. For example, U.S. Pat. No.6,421,111 discloses a multiple image reticle including a two dimensionalarray of spaced images, which obviates the need for rotation of thereticle to expose various levels of circuitry on a semiconductor wafer.

Similarly, U.S. Patent Application Publication No. 2004/0072083discloses a photomask including a plurality of mask patterns, each usedin an associated photolithography step and corresponding to anassociated semiconductor layer, where the mask patterns are arranged sothat the photomask is always used oriented in substantially the samedirection.

Finally, U.S. Pat. No. 5,604,059 discloses a mask structure including aplurality of duplicating first device patterns and a plurality ofduplicating second device patterns. The first device patterns are usedto expose a first part of a semiconductor pattern and the second devicepatterns are used to expose a second part of the semiconductor patternover the exposed first part.

In none of the prior art references is there disclosed the use of singlephotomask reticle having multiple versions of the same mask pattern,where different biasing is used.

It is an object of the present invention to provide a reticle thatincreases process yield and decreases turn-around time by compensatingfor process errors.

It is a further object of the present invention to provide an improvedreticle which has multiple versions of the same mask pattern withdifferent biasing.

Other objects and advantages of the present invention will becomeapparent from the following description.

SUMMARY OF THE INVENTION

It has now been found that the above and related objects of the presentinvention are obtained in the form of several related aspects, includingproviding a single reticle having multiple versions of the same maskpattern with different biasing.

A reticle according to an exemplary embodiment of the present inventionincludes at least two duplicate mask patterns each having a differentbias.

A reticle according to another exemplary embodiment of the inventionincludes a first mask pattern, a second mask pattern and a third maskpattern, each of the first mask pattern, second mask pattern and thirdmask pattern being duplicates of one another and having a differentbias.

The first mask pattern may be formed at a central region of the reticle,the second mask pattern may be formed adjacent to the first mask patternat a side portion of the reticle, and the third mask pattern may beformed adjacent to the first mask pattern at another side portion of thereticle.

The first mask pattern may have no bias, the second mask pattern mayhave a negative bias, and the third mask pattern may have a positivebias.

A reticle according to another exemplary embodiment of the inventionincludes a first set of a plurality of duplicate mask patterns and asecond set of a plurality of duplicate mask patterns, each of the maskpatterns in each set having a different bias.

The first set of a plurality of duplicate mask patterns may include afirst mask pattern, a second mask pattern and a third mask pattern, eachof the first mask pattern, second mask pattern and third mask patternhaving a different bias.

The second set of a plurality of duplicate mask patterns may include afourth mask pattern, a fifth mask pattern and a sixth mask pattern, eachof the fourth mask pattern, fifth mask pattern and sixth mask patternhaving a different bias.

A method of forming a reticle according to an exemplary embodiment ofthe invention includes providing a blank reticle, and forming at leasttwo duplicate mask patterns in the blank reticle, each of the at leasttwo duplicate mask patterns having a different bias.

The step of forming at least two duplicate mask patterns may include thesteps of exposing a photosensitive resist material layer to light toform an image corresponding to the at least two duplicate mask patternshaving different biases, removing portions of the photosensitive resistmaterial layer to expose corresponding portions of an opaque materiallayer below the photosensitive resist material layer, and etching theexposed portions of the opaque material layer to form the at least twoduplicate mask patterns having different biases in the blank reticle.

The step of forming at least two duplicate mask patterns may includeforming a first mask pattern, a second mask pattern and a third maskpattern, each of the first mask pattern, second mask pattern and thirdmask pattern having a different bias.

The first mask pattern may be formed with no biasing, the second maskpattern may be formed with positive biasing and the third mask patternmay be formed with negative biasing.

A method of forming a semiconductor layer of a semiconductor deviceaccording to an exemplary embodiment of the invention includesinterposing a reticle between an energy source and a semiconductorwafer, the reticle comprising at least two duplicate mask patterns eachhaving a different bias, and passing energy through one of the at leasttwo mask patterns using the energy source to form an image on thesemiconductor wafer, the one of the at least two duplicate mask patternsbeing chosen based on a required bias.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and related objects, features and advantages of the presentinvention will be more fully understood by reference to the following,detailed description of the preferred, albeit illustrative, embodimentof the present invention when taken in conjunction with the accompanyingfigures, wherein:

FIGS. 1A-1C are vertical sectional views showing various steps of amethod of forming a conventional photomask;

FIGS. 2A-2C are vertical sectional views showing various steps of amethod of forming another conventional photomask;

FIG. 3 is a plan view of a conventional mask pattern formed on a reticleplate;

FIG. 4 is a plan view of multiple duplicate mask patterns havingdifferent biases formed on a reticle according to an exemplaryembodiment of the present invention;

FIG. 5 is a plan view of multiple duplicate mask patterns havingdifferent biases formed on a reticle according to another exemplaryembodiment of the present invention;

FIGS. 6A-6D are vertical sectional views showing various steps of amethod of manufacturing a reticle having multiple duplicate maskpatterns with different biases according to an exemplary embodiment ofthe invention;

FIG. 7 is a plan view of a shuttle plane over a reticle having multipleduplicate mask patterns with different biases according to an exemplaryembodiment of the invention; and

DETAILED DESCRIPTION OF THE INVENTION

The present invention generally relates to the use of multiple copies ofthe same mask pattern on a reticle using different biases, e.g., +5 nm,0 nm, and −5 nm. The invention is equally applicable to different rangesand number of copies, as long as two or more copies have differentbiases on the same photomask. This example would allow a photomaskcustomer/semiconductor manufacturer to choose three (or more)alternative masks patterns depending on the biasing that is appropriatefor the particular stepper equipment for which the reticle is to beused. In essence, multiple field biases offer the end user a measure of“tuning” for their imaging systems.

In various exemplary embodiments of the invention, multiple maskpatterns are formed on a reticle plate. Each mask pattern is duplicatedany number of times on the plate, with each duplicate mask patternhaving a different bias. For example, a first mask pattern on the platecan have a bias of 0 nm, a duplicate second mask pattern can be formedalong side the first mask pattern with a bias of +5 nm, and a duplicatethird mask pattern can be formed along side the first mask pattern witha bias of −5 nm. The number and location of the various patternsrelative to each other and the relative biases are provided merely as anillustrative example and are not intended to limit the scope of thepresent invention. Thus, each mask pattern can have any suitable biasthat satisfies process parameters required by the customer. By way ofillustration, suitable biases may be (−10 nm, 0 nm, +10 nm), (−15 nm, 0nm, +15 nm) and (−20 nm, 0 nm, +20 nm). The various exemplaryembodiments of the invention are not restricted to 2-3 duplicates of asingle pattern, and any number of duplicate patterns having differentbiases that can fit on a single reticle can be implemented. Further, thebias does not have to be restricted to a plus bias and a negative biasdisposed around a central zero bias, but can be one sided (e.g., 0 nm,+5 nm, +10 nm), or asymmetric (e.g., −5 nm, 0 nm, +5 nm, +10 nm) and canbe any incremental value (e.g., +1 nm, +2 nm or −7.5 nm, +2.5 nm, +12.5nm).

Further, in various exemplary embodiments, the duplicate reticle maskpatterns can be laid out on the reticle plate in any suitable manner.For example, a first group of duplicate mask patterns can be formed onthe plate along with a second group of duplicate mask patterns, so thateach layer of the semiconductor device associated with a duplicate maskpattern can be formed using multiple biases. Further, the duplicate maskpatterns having the different biases can be formed on the same reticlewith mask patterns that are not formed in duplicate. In this case,preferably only important and time sensitive masks would be formedmultiple times with different biases, and other masks that are not ascrucial would not be formed in duplicate. Of course, the application ofthe present invention is not intended to be limited to only importantand time sensitive masks. Further, a first group of duplicate maskpatterns can be formed on the plate along with a second group ofduplicate mask patterns, with the first group being oriented in a firstdirection and the second group being oriented in a second direction.Similarly, any number of groups of one or more mask patterns that canfit on the reticle can be used, with any appropriate combination ororientation as long as at least one group has at least two members withdifferent biases.

FIGS. 3 and 4 are provided to explain the general concept of variousexemplary embodiments of the present invention. FIG. 3 illustrates aconventional mask pattern 110 formed on a reticle 100. The mask pattern110 is biased 0 nm, i.e., not biased, so that the exposure process toform a semiconductor layer using the reticle 1 is susceptible to processerrors. For example, the mean to nominal specification of thesemiconductor layer formed using the reticle 100 may be +10 nm due toprocess errors. Any “non-repairable” defect in the writing area of thereticle will result in a repeat of the value-added steps of the reticlemanufacturing process, making them non-valued added cost adders.

FIG. 4 illustrates an example of multiple mask patterns 210, 220 and 230formed on a reticle 200 according to an exemplary embodiment of thepresent invention. In the present embodiment, the reticle 200 includesthree duplicate mask patterns having different biases. However, anynumber of duplicate mask patterns can be formed depending on the overallarea of the reticle and the capabilities of the stepper used to exposethe semiconductor device layers. The multiple mask patterns include afirst mask pattern 210, a second mask pattern 220 and a third maskpattern 230. The first mask pattern 210 is formed in the middle regionof the reticle 200, the second mask pattern 220 is formed adjacent tothe first mask pattern 210 at one side region of the reticle 200, andthe third mask pattern 230 is formed adjacent to the first mask pattern210 at another side region of the reticle 200. The first, second andthird mask patterns 210, 220 and 230 are duplicate mask patterns thatcan be used to form the same semiconductor layer, each having adifferent bias. The appropriate biasing of each duplicate mask pattern210, 220 and 230 is based on customer latitude. For example, if the meanto nominal specification is +10 nm, the appropriate biasing may be 0 nmfor the first photomask pattern 210, +10 nm for the second photomaskpattern 220 and −10 nm for the third photomask pattern 230. Thus, thecustomer can choose from the three mask patterns 210, 220 and 230 theappropriately biased mask pattern that compensates for the processerrors that occur during the semiconductor device fabrication steps. Thechoice of which photomask pattern has which bias is not a criticalaspect of the present invention, such that any suitable order may bechosen. Other amounts of biasing may also be selected within the scopeof the present invention.

The reticle 200 illustrated in FIG. 4 affords the customer greaterflexibility regarding optimization of the photolithography processresults. As an example, the customer may choose one of the mask patternsthat compensates for manufacturing tendencies, but for some reasonresults in a single defect killer. The customer then has two other maskpatterns to choose from that avoids the killer defect, and which at thesame time provides appropriate biasing within manufacturing tolerances.The mask pattern that avoids killer defects can be used in conjunctionwith appropriate biasing of the stepper equipment to optimize thephotolithography process.

FIG. 5 illustrates multiple mask patterns formed on a reticle accordingto another exemplary embodiment of the present invention. In the presentembodiment, the reticle 300 includes two sets of three duplicate maskpatterns, each duplicate pattern in each set having a different bias. Asshown in FIG. 5, the reticle 300 includes a first set 310 of maskpatterns and a second set 320 of mask patterns. The first set 310 ofmask patterns includes a first mask pattern 330, a second mask pattern340 and a third mask pattern 350. The second set 320 of mask patternsincludes a fourth mask pattern 360, a fifth mask pattern 370 and a sixthmask pattern 380. The first mask pattern 330 is formed in the middleregion of the reticle 300, the second mask pattern 340 is formedadjacent to the first mask pattern 330 at one side region of the reticle300, and the third mask pattern 350 is formed adjacent to the first maskpattern 330 at another side region of the reticle 300. Similarly, thefourth mask pattern 370 is formed in the middle region of the reticle300, the fifth mask pattern 380 is formed adjacent to the fourth maskpattern 370 at one side region of the reticle 300, and the sixth maskpattern 380 is formed adjacent to the fourth mask pattern 360 at anotherside region of the reticle 300. The first, second and third maskpatterns 330, 340 and 350 in the first set 310 of mask patterns areduplicate mask patterns that can be used to form the same semiconductorlayer, where each of the first, second and third mask patterns 330, 340and 350 has a different bias. Similarly, the fourth, fifth and sixthmask patterns 360, 370 and 380 in the second set 320 of mask patternsare duplicate mask patterns that can be used to form anothersemiconductor layer, where each of the fourth, fifth and sixth maskpatterns 360, 370 and 380 has a different bias. Of course, the presentinvention is not limited to two sets of duplicate mask patterns havingdifferent biases. Any number of sets can be disposed on the reticle aslong as each set contains at least two duplicate mask patterns havingdifferent biases. Preferably, each set would contain at least threeduplicate mask patterns, where one pattern has no bias, one pattern hasnegative bias (e.g., −5 nm, −10 nm, −15 nm, −20 nm, etc.) and onepattern has positive bias (e.g., +5 nm, +10 nm, +15 nm, +20 nm, etc.).

FIGS. 6A-6D show various steps of a method of manufacturing a reticlehaving multiple duplicate mask patterns with different biases accordingto an exemplary embodiment of the invention. As shown in FIG. 6A, blankreticle 400 is comprised of a transparent material layer 410, an opaquelayer 420 and a photosensitive resist material layer 430. Thetransparent material layer 410 is preferably made of quartz. The opaquelayer 420 is formed on the transparent material layer 410 and is formedof a layer of Cr opaque material 422 and an integral layer of CrO ARmaterial 424 formed on top of the layer of Cr opaque material 422. Thelayer of photosensitive resist material 430 resides on top of the opaquematerial layer 420. The photosensitive resist material 430 is typicallya hydrocarbon polymer, the various compositions and thicknesses of whichare well known in the art. The desired pattern of opaque material 420 tobe created on the reticle 400 may be defined by an electronic data fileloaded into an exposure system which typically scans an electron beam(E-beam) or laser beam in a raster fashion across the blank reticle. Inexemplary embodiments of the invention, the data for each of the layersor mask patterns on the reticle can be duplicated and biased to producemultiple duplicate mask patterns having different biases in the finalreticle 400. As the E-beam or laser beam is scanned across the blankreticle, the exposure system directs the E-beam or laser beam ataddressable locations on the reticle as defined by the electronic datafile. The areas of the photosensitive resist material that are exposedto the E-beam or laser beam become soluble while the unexposed portionsremain insoluble. As shown in FIG. 6B, after the exposure system hasscanned the desired image onto the photosensitive resist material, thesoluble photosensitive resist is removed by means well known in the art,and the unexposed, insoluble photosensitive resist material 430 remainsadhered to the CrO AR material 424. Accordingly, the remainingphotosensitive resist material 430 forms patterns including patterns 432that duplicate with different biasing.

As illustrated in FIG. 6C, the exposed opaque material layer 420 nolonger covered by the photosensitive resist material 430 in the reticle400 is removed by a well known etching process, and only the portions ofthe opaque material layer 420 residing beneath the remainingphotosensitive resist material 430 remain affixed to quartz substrate410. Accordingly, the duplicating multiple patterns 432 with differentbiases in the photosensitive resist material 430 are transferred to theopaque material layer 420 to form corresponding multiple duplicatingmask patterns 422 in the opaque material layer 420. This initial or baseetching may be accomplished by either a wet-etching or dry-etchingprocess both of which are well known in the art.

As shown in FIG. 6D, after the etching process is completed thephotosensitive resist material 430 in the reticle 400 is stripped awayby a process well known in the art.

In the various exemplary embodiments of the present invention in which areticle having multiple duplicate masks with different biases is used toprocess a semiconductor layer, various issues may need to be addresseddepending on the particular stepper being used to expose thesemiconductor layer through the reticle. For example, one issue is thatradial error may dominate uniformity/registration gains related toreduced field size. Another issue is that spherical aberration of thescanner lens may be too large when overlaying smaller fields to largerfields. Still another issue is that the scanner shuttle plane may be toosmall to adequately cover all the multiple duplicate mask patterns. Thisissue is illustrated in FIG. 7. FIG. 7 shows a shutter 500 of a scannerconcentric to the center line of the reticle plane CL of a reticle 600having three duplicate mask patterns with different bias. Due to theshutter limitations, the image fields may need to be rotated 90°, whichwould allow for use of any one of the three fields of the reticle 600.

Now that the preferred embodiments of the present invention have beenshown and described in detail, various modifications and improvementsthereon will become readily apparent to those skilled in the art. Forexample, the present invention is not limited to CoG photomasks, butalso may be applied to other types of binary photomasks. Similarly, thepresent invention is not limited to EAPSM, but may also apply to othertypes of phaseshift photomasks, including by way of example, but notlimited to, AAPSM (alternating aperture phase shift mask). Furthermore,application of the present invention is not limited to reticles havingmultiple versions of only one mask pattern with different biases. Itcould also apply to reticles having multiple versions of multiple maskpatterns where each version of these mask patterns have differentbiases. Further, the inventive concept of multiple duplicate maskpatterns having different biases to improve yield is not solelyapplicable to scanner technology. The concept is applicable to almostany microlithography approach. The present embodiments are therefore tobe considered in all respects as illustrative and not restrictive, thescope of the invention being indicated by the appended claims, and allchanges that come within the meaning and range of equivalency of theclaims are therefore intended to be embraced therein.

1. A reticle comprising a first mask pattern, a second mask pattern anda third mask pattern, each of the first mask pattern, second maskpattern and third mask pattern being duplicates of one another andhaving a different bias.
 2. The reticle of claim 1, wherein the firstmask pattern is not biased, the second mask pattern has a negative bias,and the third mask pattern has a positive bias.
 3. The reticle of claim1, wherein the first mask pattern has a bias of 0 nm, the second maskpattern has a bias of +5 nm, and the third mask pattern has a bias of −5nm.
 4. The reticle of claim 1, wherein the first mask pattern has a biasof 0 nm, the second mask pattern has a bias of +10 nm, and the thirdmask pattern has a bias of −10 nm.
 5. The reticle of claim 1, whereinthe first mask pattern has a bias of 0 nm, the second mask pattern has abias of +15 nm, and the third mask pattern has a bias of −15 nm.
 6. Thereticle of claim 1, wherein the first mask pattern has a bias of 0 nm,the second mask pattern has a bias of +20 nm, and the third mask patternhas a bias of −20 nm.
 7. The reticle of claim 1, wherein the bias ofeach of the mask patterns is a negative bias.
 8. The reticle of claim 1,wherein the bias of each of the mask patterns is a positive bias.
 9. Thereticle of claim 1, wherein the first mask pattern has a zero bias, andat least the second and third mask patterns have a positive bias. 10.The reticle of claim 1, wherein the first mask pattern has a zero bias,and at least the second and third mask patterns have a negative bias.11. A reticle comprising at least two duplicate mask patterns eachhaving a different bias.
 12. A reticle comprising a first set of aplurality of duplicate mask patterns and a second set of a plurality ofduplicate mask patterns, each of the mask patterns in each set having adifferent bias.
 13. The reticle of claim 12, wherein the first set of aplurality of duplicate mask patterns comprises a first mask pattern, asecond mask pattern and a third mask pattern, each of the first maskpattern, second mask pattern and third mask pattern having a differentbias.
 14. The reticle of claim 13, wherein the second set of a pluralityof duplicate mask patterns comprises a fourth mask pattern, a fifth maskpattern and a sixth mask pattern, each of the fourth mask pattern, fifthmask pattern and sixth mask pattern having a different bias.
 15. Amethod of forming a recticle comprising the steps of: providing a blankreticle; and forming at least two duplicate mask patterns in the blankreticle, each of the at least two duplicate mask patterns having adifferent bias.
 16. The method of claim 15, wherein the step of formingat least two duplicate mask patterns comprises the steps of: exposing aphotosensitive resist material layer to light to form an imagecorresponding to one of the at least two duplicate mask patterns havingdifferent biases; removing portions of the photosensitive resistmaterial layer to expose corresponding portions of an opaque materiallayer below the photosensitive resist material layer; and etching theexposed portions of the opaque material layer to form one of the atleast two duplicate mask patterns having different biases in the blankreticle.
 17. The method of claim 15, wherein the step of forming atleast two duplicate mask patterns comprises forming a first maskpattern, a second mask pattern and a third mask pattern, each of thefirst mask pattern, second mask pattern and third mask pattern having adifferent bias.
 18. The reticle of claim 17, wherein the first maskpattern is not biased, the second mask pattern has a negative bias, andthe third mask pattern has a positive bias.
 19. A method of forming asemiconductor layer of a semiconductor device comprising the steps of:interposing a reticle between an energy source and a semiconductorwafer, the reticle comprising at least two duplicate mask patterns eachhaving a different bias; and passing energy through one of the at leasttwo duplicate mask patterns using the energy source to form an image onthe semiconductor wafer, the one of the at least two duplicate maskpatterns being chosen based on a required bias.
 20. The method of claim19, further comprising etching the semiconductor wafer using the imageformed on the semiconductor wafer to form the semiconductor layer. 21.The method of 19, wherein the at least two duplicate mask patternscomprises a first mask pattern, a second mask pattern and a third maskpattern, each of the first mask pattern, second mask pattern and thirdmask pattern having a different bias.
 22. The method of claim 21,wherein the first mask pattern is not biased, the second mask patternhas a negative bias, and the third mask pattern has a positive bias. 23.The method of claim 19, wherein the energy source is a stepper.